fix helm schema validation for executor value

[chrisfregly]

Closes: #54673.

Updating the Airflow Helm Chart schema validation for the executor field to allow custom executors to be specified along with the existing officially supported Airflow executors.

This regex change checks each supplied executor in the list to ensure it matches the following:

<optional.python.package.path.><RequiredExecutorName>Executor

---

^ Add meaningful description above
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[boring-cyborg]

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[potiuk]

Good idea!

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.